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Tuesday, July 19, 2011

Going Cellular with LXI

Test and measurement instruments with the LAN eXtensions for Instrumentation or LXI standard use LAN or Ethernet for remote connectivity (click here for more info on LXI). The Ethernet standard is widely used all over the globe and because of its wide use there is a wide array of low cost off the shelf networking products that make connecting to LXI instruments from anywhere at any time with various types of computing devices possible. The wide array of off the shelf LAN compatible network products available today provides a major advantage for LXI in long distance testing, long duration testing, distributive testing, and various DAQ applications because of the low cost and connection flexibility they provide. In this blog post we are going to look one such off the shelf networking device, a cellular router, and the benefits it provides for testing.

The router you use at home uses an Ethernet connection to access the internet. A cellular router on the other hand uses a cellular provider’s network to access the internet. This means if you connect an LXI instrument to the cellular router that instrument can now be accessed from any cellular network or WiFi network or Ethernet network that is connected to the internet. This provides four big test advantages:

It gives you the ability to easily setup long distance remote testing sites from almost anywhere around the globe as long as it is in range of a cellular tower.

It gives you the ability to run a distributed test with one remote controller.

It allows you to access measurement data or control instruments from almost anywhere around the globe with various computing devices such as a laptop, smart phone, or server.

It allows you to perform remote testing in a moving vehicle as long as the vehicle remains in the range of cellular network towers.

As explained above and illustrated in the figure below, cellular routers make LXI instrument access almost totally ubiquitous.

No cellular provider is going to let you use their network for free so you do need to purchase a mobile broadband USB stick or a WiFi broadband tethering device along with a monthly data plan. The USB broadband device can be connected directly to the cellular router or the WiFi broadband tethering device can be connected over WiFi. Of course with the WiFi broadband tethering device you could just use a basic WiFi router that has a bridge mode.

There are some security hurdles and concerns you should be aware of when using any router. Consumer routers, including cellular routers, in default mode assume all the devices connected directly to them are client devices and not servers. Because of this they block all external connection requests from client devices outside of their local network. This is a big problem because LXI instruments are servers (that is how they host a web page) so computers or controllers external to the router's network that try to connect to them will be blocked by the router. To overcome this you need to access the router's port forwarding feature or DMZ feature. Port forwarding allows you to specify certain network ports to allow connection requests to come in on and which IP address on the router’s local network to forward them to. You can also use the router's DMZ feature which allows you to forward all incoming connection requests, regardless of port, to a specified local IP address. Using port forwarding and DMZ features also opens up security concerns. Any opening you make into the router to access an instrument is open to anybody on the internet. This can be especially troublesome to LXI instrument running a Window's based PC operating system because they are vulnerable to cyber attacks. The port forwarding method is more secure than DMZ because it allows you to use obscure port numbers that are not used by the general public and then forward the connection request or message to a more commonly used port on the instrument such as port 80 or 5025. For more information on increasing security when accessing instruments through a router shot me an email.

When purchasing a cellular router you want to pay attention to its list of compatible broadband devices. Also be aware that the cellular provider that you purchase the broadband device from probably does not guarantee that their device will work on a cellular router so if you need support help go to the manufacturer of the router. Currently the largest cellular or broadband router maker is cradlepoint, you can check them out at http://www.cradlepoint.com/

11 comments:

One important note that I forgot to include in this post is getting a static IP address. By default the wireless carrier will continually change the IP address of the mobile broadband device. This is undesirable since you need to know the IP address of the broadband device to connect and control the instrument(s). To solve this hurdle you can contact the cellular carrier and request a static IP. There may be a cost associated with it, for instance in the US Verizon charges a one time $500 fee for a static IP address.

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